This apparatus and method are an improvement in the dip forming process for increasing the diameter of metal wire or rods. The dip forming process is sometimes referred to in the prior art as a form of coating or casting. Casting usually implies the use of a die. However, xe2x80x9ccastingxe2x80x9d is known in the art to also mean producing a metallic object with a preferred shape by running it through a molten bath and allowing the molten metal to solidify on the initial metal wire or rod. The present apparatus includes a block of metal that will be used as the coating material (referred to as the xe2x80x9csource block of coating materialxe2x80x9d) to add diameter to the metal wire or rods (referred to as xe2x80x9ccore materialxe2x80x9d). The source block of coating material is housed within a hollow receptacle (known in the art as a xe2x80x9cvesselxe2x80x9d or xe2x80x9ccruciblexe2x80x9d) and machined to include a hole that closely fits the core material that will pass through the block of coating material. The apparatus includes heating elements positioned on the exterior of the crucible such that only the upper portion of the source block of coating material housed within it will become molten while the heating elements are active and the lower portion of the source block will remain solid. The exact position of the heating elements on the crucible will vary with the size and dimensions of both the crucible and the source block, as well as with the amount of energy supplied to the heating elements.
The method includes passing the core material to be coated upward through the machined hole in the source block of coating material. The source block of coating material is located within the crucible and during operation exists in three physical states: (1) solid, in the base region of the source block of coating material where a machined channel or hole closely fits the core material; (2) solid/molten metal interface, where the core material and the molten metal from the source block converge; and (3) molten metal from the source block, for coating the core material as it moves upward through the crucible.
The core material passes upward through the machined hole within the solid portion of the source block of coating material before it contacts the molten metal that will coat the core material. A problem with the dip forming process is that small particles become entrained on the core material and form inclusions in the coated product or contaminate the molten coating material. This problem is eliminated in the subject apparatus where the closeness of fit between the core material and the hole machined within the source block of coating material provide a guide and seal to eliminate this problem. This seal prevents the core material from entering the crucible with entrained particles that may result in inclusions in the coated product or contamination of the molten metal used in the coating process.
The prior art has solved the problem of small particle entrainment by use of a bushing member to seal the entrance port for the core material. Use of such a bushing member has introduced new problems with the process. The dip forming processes have required that the bushing member be of different composition than the molten metal as described in U.S. Pat. No. 3,995,587 and other U.S. Patents referenced therein.
The closeness of fit between the solid portion of the source block and the core material is intended to serve the purpose of the bushing used in the prior art. The fit should be close enough to remove small particles that may become entrained on the core material and close enough to prevent the molten metal from entering the hole in the source block while the core material moves through the dip form processing apparatus, but not so close as to bind the core material within the source block.
When the bushing has a different metal composition relative to the metal that is used to coat the core material, the integrity of the process is at risk. Reactive metals, such as titanium and zirconium, readily dissolve other metals. Reactive metals used to coat the core material may dissolve the bushing on contact and may compromise the structural integrity of the crucible. The bushing otherwise effects the structural integrity of the crucible by being subject to physical wear by the moving core material. The bushing member is embedded in the vessel or crucible bottom and thus affects the ability of the crucible to hold molten metal over time. When the bushing member breaks down in the presence of reactive metals it becomes a new source of inclusions on the core material and a new source of contamination of the coating material.
The present apparatus and method avoid problems with the bushing by using the closeness of fit between the core material and the source block of coating material to prevent entrainment of small particles on the core material. Closeness of fit coupled with steady movement of the core material through the apparatus prevents the molten metal coating material from leaking out of the crucible.
The primary object of this invention is to provide a method for increasing the diameter of core material that does not require a bushing member at the entrance port of the crucible in order to eliminate the break down of such members particularly when reactive metals are used and to avoid the subsequent entrainment of particles within the cast product.
Another object of this invention is to provide an apparatus to allow the elimination of a bushing member from the entrance port of the crucible by utilizing a solid portion of the coating material as a guide and seal at the entrance port for the core material.
Another object of this invention is to heat and melt only the top portion of the source block material creating a source block/core material interface while the bottom portion of the source block remains solid.
This apparatus and method are an improvement for increasing the diameter of core material, such as metal and alloy wire and rods, by use of a molten metal pool. The method encompasses the startup and batch, intermittent, or continuous operation of coating and casting to increase diameters of core materials, especially for applying reactive metal coatings. The core material is moved upward through a source block of coating material. The invention eliminates the need for a bushing member at the entrance port and, thus, eliminates potential contamination and molten metal sealing problems due to bushings.
During operation the source block of coating material serves as: (1) a solid component core material entrance guide; (2) the solid/molten interface; and (3) the molten metal coating material. The invention is especially applicable for coating and increasing the diameter of reactive metal wire and rods because the same composition reactive metal source coating block material is used as the wire entrance guide, seal, and molten metal source for wire coating. The invention is applicable for cold-wall copper crucibles (both bottomless and casting crucibles with bottoms), ceramic crucibles, or any other containment crucible appropriate for the type of metal or alloy being melted. The system can be under vacuum, partial vacuum, atmospheric pressure, or positive pressure that is appropriate for the metal or alloy being melted.